1. Field of the Invention
The invention relates to a method and a safety system for a locking device for a motor vehicle.
2. Prior Art
From the prior art it is known to use serial data protocols of a bus technology in the motor vehicle for data transfer between electronically controlled devices. Thus by way of example the individual body control devices are linked, such as the central body electronics, combination instruments and control devices in the doors. From the central body electronics, a central control device in the motor vehicle, trigger signals are generated more particularly for the central locking function and are transferred to the executing control devices by means of a serial data protocol. The locking function is thereby dependent on these trigger signals.
Furthermore it is known in the event of a complete breakdown of the bus system to switch the door control devices over automatically into an emergency operating mode in order to enable the functions pertaining to safety which are dependent on being triggered. It has however been seen that even with a breakdown of one part of the electronics which are connected through the bus (central control device or further instruments of the motor vehicle connected thereto) important or even all functions of the displacement systems can be blocked because a failed electronics unit could no longer supply the data which was necessary to generate the trigger signals. Such emergency operating modes for window lifters are known for example from EP 1 060 922 A or DE 199 28 101 C2.
Furthermore the technical functioning of the displacement systems is dependent on the functional ability and reliability of the control devices. Breakdown situations which lead to a partial failure of the control electronics run the risk of generating parasitic resistances which clearly reduce insulation between two conductor paths of the electronics of the door control device. Parasitic resistances caused in this way can have values of some hundred ohms. If this resistance arises between a control connection of a power switch and a fixed potential, more particularly the battery voltage or the earth connection, then this can lead to undesired control of the power switch and consequently to an undesired adjustment of the displacement device.
The breakdown of parts of the vehicle electronics, more particularly the bus system or the control device through crash effects can lead to the undesired displacement of the displacement device in the emergency accident situation and to additional dangers.